We report our data using what is known as a control chart. There are four elements on the chart. 1) The blue diamonds: these are the actual data points for each month. They depict the event rate as defined on the vertical axis. 2) and 3): The dotted red lines: these are the upper and lower control limits. They are scientifically calculated to represent the statistical range within which normal random variation occurs in a stable system. 4) The solid red line. This is the average of the blue diamonds for that time frame. As long as the blue diamonds are within the dotted red lines, the system being measured is a stable one. There are certain patterns of blue diamond configuration (e.g. diamonds outside the control limits), that mean something in the system has changed. This is called special cause variation and will usually involve a deeper investigation as to why the new pattern of variation. Each control chart contains an arrow which indicates the desired change direction. For most harm events, the desired direction is down (i.e. less harm is better). For other measures (compliance rates, days between harm events) the desired direction is up.